The present invention relates to implantable stimulators and, specifically, methods and systems for delivering stimulation through multiple output channels.
Multi-channel stimulators are used in a number of implantable medical devices. For example, a cochlear device for restoration of hearing is an exemplary device which uses a multi-channel stimulator. Representative prior art cochlear implant systems are disclosed in U.S. Pat. Nos. 4,592,359; 4,947,844; 5,776,172; and 6,067,474, all of which are herein incorporated by reference. Another use of implantable, multi-channel stimulators include those for spinal cord stimulation for treating intractable pain. Representative spinal cord stimulation (and electrode) systems are disclosed in International Publication Number WO 02/09808 A1 and in U.S. Pat. Nos. 3,646,940; 3,724,467; and 3,822,708, all of which are herein incorporated by reference.
Such multi-channel, implantable stimulators presently have the capability of driving up to 16 electrodes and have increased processing capability. The large number of channels and advanced processing capability typically consume more power than devices having fewer channels. The long-term trend is toward using more channels while more processing capability is added. In cochlear applications, more channels can be used to provide higher resolution of perceived sounds. For spinal cord stimulation, having more channels affords greater flexibility in shaping current stimulation fields after the lead is implanted so that the initial lead placement is less critical for successfully inducing paresthesia to overlap the regions of pain.
While enhanced processing is desired, a concurrent goal is to decrease the size of the implanted device while making the battery last longer. Making the device smaller is advantageous for a number of reasons. One reason is that implantation can be less invasive and, hence, less susceptible to infection. Another reason is that the device is less obtrusive once implanted under the skin, within the skull, or within the body.
Thus, it is evident that there is a need for systems and methods of reducing the space taken up by circuitry in an implantable stimulator. The space thus saved can be used to reduce the overall size of the implanted device or, alternatively, used to implant a larger battery in the saved space to enable more channels, more processing power or longer device life.